(1) Field of the Invention
The present invention relates to optical devices and in particular to systems and methods to precisely move and control the position of lens systems of an optical device as e.g. cameras using electrical sensors to measure the actual position of the lens system.
(2) Description of the Prior Art
The positions of lenses e.g. in conjunction with autofocus (AF) cameras have to be controlled with utmost precision. Lenses have to be moved rapidly and precisely to the optimal position. Various and quite different implementations are in place to achieve such a positioning.
U.S. patent (U.S. Pat. No. 5,652,928 to Baxter et al.) discloses to use an auto ranging device to determine a lens destination focus position in term of a target number of signal pulses from a lens motion sensor photo-interruptor. A lens-drive motor is initially driven at maximum speed by a 100% pulse width modulated drive signal. At a fixed number of signal pulses in advance of the target, the average motor speed is calculated and a reduced pulse with modulated drive signal, determined based on the calculated motor speed, is applied to the drive motor to cause the lens to arrive at a uniform speed at a near destination focus position that is suitable for application of a standard motor stopping routine. During the motor stopping routine, the motor is initially “plugged” (reverse polarity drive signal) and the signal pulse period is monitored until a predetermined period is reached. At this point, the plug is removed and an electrical brake (short circuit) is applied to the motor to bring the lens to a rest at the destination focus position.
U.S. patent (U.S. Pat. No. 7,006,137 to Kim et al.) teaches a micro mode executing apparatus of a digital still camera having an image sensor and a focus-controlling lens connected to a focus driving motor and a spindle of the motor, thereby controlling an optical length within the range of a fixed barrel structure. A focus lens is positioned on the same optical axis as the image sensor and is secured to one end of the rotating axis of the spindle. A first biasing member is connected to the focus lens and the motor, and has a constant biasing force; and a second biasing member is provided for positioning the motor on the first step region for applying a biasing force in a lateral direction.
There are more known patents dealing with moving and positioning of lenses in optical devices:
U.S. patent (U.S. Pat. No. 6,603,929 to Ishikawa et al.) teaches a camera system comprising: a first focus detection unit, which detects the focusing condition of an image-taking optical system; a second focus detection unit, which detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit; and a control circuit, which controls a stepping motor for driving a focus lens. The control circuit performs closed loop control for driving the stepping motor based on the output of a rotation detector, which detects the rotation phase of the stepping motor, when controlling the stepping motor using the information based on the output of the first focus detection unit, and performs open control for driving the stepping motor a predetermined number of steps at a time, when controlling the stepping motor using the information based on the output of the second focus detection unit. The autofocus process is thereby made high in speed and high in precision at the same time.
U.S. patent (U.S. Pat. No. 7,003,222 to Murakami) discloses a camera that maintains accuracy of stop position in accordance with the state of an image-taking optical system and allows driving of a focus lens to a target position in a short time period. The camera comprises a motor that drives the focusing lens, and a controller, which controls the motor such that the focusing lens is stopped at the target position by performing deceleration control in accordance with a predetermined deceleration control pattern. A zoom brush is serving as a state detector, which slides over a resistor in association with movement of the zooming lens to detect the position of the zooming lens. The controller changes the deceleration control pattern in accordance with the state of the image-taking optical system detected by the state detector.
U.S. patent (U.S. Pat. No. 5,623,708 to Watanebe) discloses a camera including an autofocus adjustment device. The autofocus device comprises a lens and camera body. The lens is comprised of a shooting lens, a lens information circuit, and a lens movement mechanism. The camera body has a main mirror, a submirror, an AF module, a sensor drive circuit, a controller, a lens drive control circuit, and motor. The autofocus adjustment device uses image plane movement velocity for the determination of a moving object and uses focus position change velocity in lens drive control.